Batteries in the form of button cells as either primary batteries (non-rechargeable) or accumulators (multiply rechargeable) are used regularly nowadays as independent and small power source in portable electronic devices requiring a long service life span, e.g. wristwatches, pocket calculators, and hearing aids. Like an ordinary battery they consist of a number of galvanic elements in parallel which, on closure of the circuit, generate an electric current. These are usually placed inside a cylindrical can which is then closed by a circular cap and a seal, the latter of which providing electric insulation between can and cap as well as airtight closure.
In state-of-the-art designs, the parallel series of the galvanic elements consists of concentric, hollow metal toroids with parallel, vertical walls. Each of those is coated on the inside with a layer of separator material (i.e. the salt bridge) and contains the cathode material. The anode material is placed between the toroids. To allow an exchange of ions between anode and cathode material, the vertical walls of the toroids are punctured by holes which are closed from the interior by the layer of separator material. Thus, the toroids can be conductively connected to the side and bottom of the can, which then become the positive pole, while the rings of anode material are conductively linked to the interior surface of the cap, creating the negative pole.
The design described above has many disadvantages. Firstly, the interior resistance of any galvanic cell is inversely proportional to the surface area of the separator layer in contact with both anode and cathode material. Puncturing the walls of the toroids to allow access of the anode material to the separator layer reduces the area where the chemical reaction can take place. Any working design is thus a compromise, balancing wall area against hole area to optimise the production of electric current. Secondly, while a conductive connection between toroids and can is easily feasible by placing the toroids directly on the bottom or wall of the can, the conductive link between the layers of anode material and the cap is more complex. It is often achieved by a series of lamellas welded to the interior underside of the cap and extending into the anode material. While a contact between these lamellas does not restrict the mode of operation, a contact between lamella and toroid would provide a short circuit and has to be strictly avoided. This can be achieved by a non-conductive filling material placed between the lamellas, which however complicate the assembly considerably. Thirdly, the relatively small sealing area between can and cap, while initially providing an airtight seal, is easily breached, allowing anode and insulating material to be spilled and reducing battery performance.